This invention relates to sealing and bearing means by use of ferrofluid which is suitable for rotary means requiring low noises and high accuracy.
First of all, a principle of the conventional sealing and bearing means by use of ferrofluid will be described with reference to FIG. 1. Numeral 1 is a rotary shaft and numeral 2 is a cylindrical magnet for enclosing the rotary shaft 1 concentrically. The cylindrical magnet 2 is provided, at its both ends 2a and 2b, with a flange having openings 3 and 4 for passing the rotary shaft 1. Numerals 5 and 6 are gaps for sealing, which are formed between the faces of the openings 3 and 4 and the surface of the rotary shaft 1. Numeral 7 is a ferrofluid filled inside the magnet 2, which is retained upon the overall surface of the rotary shaft 1 by means of attraction of magnetic flux formed concentratedly within the gaps 5 and 6. Numeral 8 is a housing. The both ends 2a and 2b are composed of pole pieces made of a ferromagnetic soft steel for attracting magnetic flux. Further, a cylindrical member 9 having grooves for generating the dynamic pressure of the ferrofluid is fixed with an surface of the rotary shaft 1. Further, in order to center the rotary shaft 1 by exerting effectively the dynamic pressure generated by rotation of the shaft 1, to prevent any damage of the shaft 1 in contacting with the magnet 2 and to promote an effective magnetic sealing, it is required to fix a cylindrical center member 10 consisting of a non-ferromagnetic material upon the interior of the magnet 2. The structure of such a conventional sealing and bearing means will be illustrated more fully in FIG. 2 where a thrust/radial bearing is shown.
Since the same construction as shown in FIG. 1 has the same numerals, its description will be omitted.
The housing 8 supports the magnet 2 and the pole pieces 2a and 2b by means of clamping nuts 8a and 8b. The cylindrical member 9 which is fixed with the surface of the shaft 1 and rotatable integrally therewith is provided, upon the surface thereof, with herringbone grooves 9a for generating the dynamic pressure of the ferrofluid. Between the cylindrical non-magnetic center member 10 fixed on the interior of the magnet 2 and the surface of the cylindrical member 9 is formed a slight gap. Numerals 11a and 11b are flange-type thrust bearings fixed with the shaft member 9. Likewise, there is formed a slight gap between the pole pieces 2a, 2b and the interior of the magnet 2, and the side surface of the center member 10.
When the rotary shaft 1 and the cylindrical member 9 fixed therewith are rotated integrally to an arrow direction, the ferrofluid 7 as a lubricant is directed to a center plane section 9b of the cylindrical member 9 due to the function of the grooves 9a for generating the dynamic pressure, and its pressure is increased in this section 9b, but decreased adjacent the gaps 5 and 6. Accordingly, in cooperation with attraction of the concentrated magnetic flux in the gap 5 and 6, outside leakage of the ferrofluid 7 is prevented.
FIG. 3 shows another example of the conventional sealing and bearing means by use of ferrofluid, in which the grooves for generating the dynamic pressure thereof are engraved on the surface of the rotary shaft 1 itself. The same construction as shown in FIG. 2 has the same numerals, but the thrust bearings 11a and 11b are removed. In this respect, it is different from the aforesaid thrust and radial bearing means.
Generally, bearings for generating the dynamic pressure of the ferrofluid as a lubricant have excellent properties such as high rotation accuracy, low noises, long durability, etc. In addition, such bearings are provided with sealing means by use of ferrofluid, so that any danger of oil leakage or oil splashing is removed. Accordingly, they may be used suitably for a clean room for producing large-scale integrated circuits, magnetic disc spindles, etc. where a completely clean environment is required.
However, the conventional sealing and bearing means are extremely complicated in structure and very difficult for making it compact, so that it is forced to become large-scale. On the other hand, when producing such grooves for generating the dynamic pressure, it is required to engrave accurate grooves of specified profile upon e.g. the surface of the rotary shaft. Namely, it requires a very high working accuracy, consequently the sealing and bearing means having such structure are very expensive in view of production cost and unsuitable for practical use.
Further, in the midst of assembling the bearing means, it has been required to inject the ferrofluid in advance into a gap between the rotary shaft and the bearing so that it may be filled fully therein. However, it is a cumbersome work.
Because of such disadvantages and inconveniences of the conventional sealing and bearing means by use of ferrofluid, it is entirely impossible to produce them in a mass production scale.